JPH07205230A - Reservoir inner pressure regulating method for injection molding machine - Google Patents

Abstract

PURPOSE:To stabilize physical properties of melted resin in a reservoir and to reduce a molding malfunction of a molded form by detecting a deviation of a screw rotating torque, detecting a change of disturbance operated at the screw in an opposite-metering direction, and accurately detecting a variation in a reservoir inner pressure. CONSTITUTION:In an injection molding machine for driving a screw at a back pressure set corresponding to a position of the screw 2 and a screw rotating speed to execute a metering step, a screw rotating torque in the metering step at the time of molding a good molded form is previously set and stored in a controller 10 of the machine corresponding to a screw position. A present value of the rotating torque is sequentially detected in the metering step. A deviation between the rotating torque of the screw 2 previously set and stored in the controller 10 of the machine corresponding to a present screw position and a present value of the torque is obtained. A set back pressure is varied based on the torque deviation. Thus, a reservoir inner pressure of an injection cylinder 1 is stabilized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for adjusting the internal pressure of a reservoir in an injection molding machine.

[0002]

2. Description of the Related Art The internal pressure of resin accumulated at the tip of an injection cylinder by the metering rotation of a screw, that is, the internal pressure of a reservoir, has a great influence on the injection pressure holding operation over several cycles after the metering step. Therefore, as much as possible, it is desirable to maintain the internal pressure of the reservoir at a constant value according to the screw position for each measuring process.

In order to achieve such an object, a pressure detector is provided at the tip of the injection cylinder, and the thrust force applied to the screw is closed-loop controlled by directly detecting the internal pressure of the reservoir. Is proposed. However, there have been problems that the structure relating to the mounting of the pressure detector is complicated, and that the pressure detector is directly exposed to the high temperature of the resin, so that failure or deterioration easily occurs.

As a result of considering such a situation, at present, a pressure detector is provided between the drive source for axially driving the screw and the screw, for example, at the base of the screw. The detected screw reaction force is detected as the internal pressure of the reservoir, and the back pressure control is performed by controlling the screw retreating speed and the screw rotation speed based on the screw reaction force. It is common to try to keep it at a constant value.

[0005]

However, the reaction force acting on the screw as a whole is actually the anti-measuring force acting on the screw as the resin in the injection cylinder is conveyed and plasticized, which is required for the measurement. This value is a combination of the reaction force in the direction and the screw retracting force generated by pure reservoir internal pressure.Even if the pressure detector collectively detects the reaction force acting on the entire screw, it is not possible to detect the internal pressure of the reservoir. I won't. The reaction force in the anti-metering direction that acts on the screw along with the conveyance and plasticization of the resin in the injection cylinder is, for example, the ease of plasticization such as whether the pellet is a virgin pellet or a recycled material, and , And various changes due to disturbances such as differences in properties such as the size and external shape of pellets.

Here, if the reaction force acting on the screw as a whole is Fa, the screw retracting force generated by the internal pressure of the reservoir is Fb, and the screw reaction force that fluctuates due to disturbance and acts on the screw in the counter-measuring direction is Fc, Fa
However, even if a predetermined reaction force Fa is applied to the screw to keep the screw retracting force Fb generated by the reservoir internal pressure constant, the screw retracting force Fb generated by the reservoir internal pressure corresponds to the screw position. There is no guarantee that it will be held at a fixed value. Even if the screw retracting force Fb generated by the internal pressure of the reservoir becomes low, Fa = Fb + Fc if the screw reaction force Fc in the anti-metering direction affected by the disturbance is increasing.
Even if the condition of is satisfied and the screw retracting force Fb generated by the internal pressure of the reservoir becomes high, if the screw reaction force Fc in the counter-measuring direction decreases, Fa = Fb + F
Since the condition of c is satisfied, and only the magnitude of the total reaction force Fa is generated, the screw retracting force F generated by the internal pressure of the reservoir is generated.
This is because the value of b is not specified. Dividing both sides of Fa = Fb + Fc by the screw cross-sectional area A gives: Fa / A = Fb / A + Fc / A Here, Fa / A is the back pressure and Fb / A is the reservoir internal pressure.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art, to eliminate the need for providing a pressure detector for directly detecting the internal pressure of the reservoir, and to keep the internal pressure of the reservoir at a constant value according to the screw position. It is to provide a method for adjusting the internal pressure of a reservoir in an injection molding machine capable of performing the above.

[0008]

SUMMARY OF THE INVENTION The present invention is an injection molding machine in which a screw is driven at a back pressure and a screw rotation speed set corresponding to a screw position to perform a measuring process. The screw rotation torque in the measuring process is set and stored in advance in the controller of the injection molding machine in correspondence with the screw position, and the current value of the screw rotation torque is sequentially detected in the measuring process, and injection molding is performed corresponding to the current screw position. The object is achieved by obtaining a deviation between a screw rotation torque preset and stored in a controller of the machine and a current value of the screw rotation torque, and changing the set back pressure based on the torque deviation.

Further, the function showing the relation between the screw reaction force generated by the screw rotation torque and the screw rotation torque, and the relation between the reservoir internal pressure and the screw position are preset and stored in the controller of the injection molding machine.
The current value of the screw rotation torque is sequentially detected in the measuring step, the current screw reaction force is obtained based on the above function, and is preset and stored in the control device of the injection molding machine corresponding to the current screw reaction force and the current screw position. The same purpose as described above was achieved by outputting the sum of the internal pressure of the reservoir and the back pressure.

In the reservoir internal pressure adjusting method as one embodiment, a function indicating the relationship between the screw reaction force generated by the screw rotation torque and the screw rotation torque is set and stored in the controller of the injection molding machine as a proportional expression.

[0011]

[Operation] The reaction force Fa acting on the screw as a whole is
It is the sum of the screw retreating force Fb generated by the internal pressure of the reservoir and the reaction force Fc acting on the screw in the anti-measuring direction that accompanies the conveyance and plasticization of the resin in the injection cylinder, which is required for the measurement. Of these, the value of Fc is affected by the disturbance, but the relationship of Fa = Fb + Fc is always established regardless of the influence of the disturbance. The reaction force Fc acting on the screw in the counter-measuring direction is caused by the resin conveyance and plasticization due to the metering rotation of the screw, and the larger the rotation torque Tr of the screw, the larger the value of Fc. , Fc is smaller when the screw rotation torque Tr is smaller, that is, Fc = a.
There is a relationship of Tr.

Therefore, the reaction force acting on the screw as a whole at the screw position Si at a certain stage of the measuring process during molding of a good product is Fai, the screw retracting force generated by the internal pressure of the reservoir at this time is Fbi, and the reaction in the counter-measurement direction is Force Fc
If i and the screw rotation torque are Tri, the following relationship holds: Fai = Fbi + Fci = Fbi + a.Tri. If the rotational torque of the screw becomes Trn at this time and a torque deviation of (Tri-Trn) is generated between the screw rotational torque Tri and the reference screw rotational torque Tri, the reaction in the anti-measurement direction at this time occurs. Since the force Fcn is a · Trn, Fci−Fcn = a · (Tr
i-Trn) pressure deviation is generated, and the screw retreating force generated by the internal pressure of the reservoir is used as a reference value Fbi.
In order to hold the screw, the force supporting the reaction force acting on the screw as a whole is changed from Fai to Fai-a. (Tri-T
rn) must be corrected.

Therefore, according to the present invention, in the injection molding machine in which the screw is driven at the back pressure Fai and the screw rotation speed set corresponding to the screw position to perform the measuring process, the screw in the measuring process at the time of molding a good product. The rotation torque Tri is set and stored in advance in the control device of the injection molding machine in association with the screw position, and the current value Trn of the screw rotation torque is sequentially detected in the measuring process, and the injection molding machine corresponding to the current screw position is detected. The deviation between the screw rotation torque Tri preset and stored in the control device and the current value Trn of the screw rotation torque is obtained, and the set back pressure is changed from Fai to Fai-a (based on the torque deviation (Tri-Trn). By changing to Tri-Trn), the screw retraction force Fbi generated by the internal pressure of the reservoir is To be constant.

That is, the present value T of the screw rotation torque
rn is the screw rotation torque Tr preset and stored in the controller of the injection molding machine in correspondence with the current screw position Si.
If it is larger than i, the screw back pressure is set Back pressure Fai
To Fai-a · (Tri-Trn), the screw retracting force Fbi generated by the internal pressure of the reservoir is held at a predetermined value, and the current value Trn of the screw rotation torque corresponds to the current screw position of the injection molding machine. Screw rotation torque Tri preset and stored in the control device
If it is smaller than the above, the screw back pressure is reduced from the set back pressure Fai to Fai-a · (Tri-Trn), and thereby the screw retreating force Fbi generated by the internal pressure of the reservoir is maintained at a predetermined value.

Further, the screw retracting force Fbi generated by the ideal reservoir internal pressure for each screw position Si is directly set in the control device of the injection molding machine, and the screw retracting force Fbi generated by the reservoir internal pressure for each position and the actual value at each position are set. Of the screw rotational torque Trn detected at the time point and the function Fcn = a · Trn showing the relation between the screw reaction force Fcn generated by the screw rotational torque Trn and the screw rotational torque Trn, Fai = Fbi + a ·
By calculating the value of Trn and outputting this value Fai as a back pressure command given to the entire screw, the screw retracting force Fbi generated by the internal pressure of the reservoir is held at the target value.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a main part of an injection molding machine of an embodiment to which a method for adjusting a reservoir internal pressure according to the present invention is applied.
Reference numeral 1 is an injection cylinder of the injection molding machine, and reference numeral 2 is a screw. The screw 2 is driven in the injection axis direction by an injection servomotor M1 which is a drive source through a drive converter 5 for converting the axial rotation of the drive source into a linear motion in the injection axis direction, and the gear mechanism 3 Via the screw rotation servomotor M2. The injection servomotor M1 is provided with a pulse coder P1 for detecting the position and movement speed of the screw 2, and the screw rotation servomotor M2 is provided with a speed detector P2 for detecting the rotation speed of the screw 2. Has been deployed.
A pressure detector 4 is provided at the base of the screw 2 to detect the reaction force acting in the axial direction of the screw 2, that is, the injection holding pressure in the injection holding process, the screw back pressure in the measuring process, and the like. It is like this.

However, the reaction force acting in the axial direction of the screw 2 means the screw retreating force Fb generated by the internal pressure of the reservoir.
Injection cylinder 1 required for weighing, not itself
It is a value obtained by combining the reaction force Fc in the anti-measuring direction acting on the screw 2 due to the conveyance and plasticization of the resin therein and the screw retracting force Fb generated by the pure reservoir internal pressure.
Among these, the screw retracting force Fb generated by the internal pressure of the reservoir is the internal pressure of the reservoir in the injection cylinder 1, that is, the resin filling the space formed between the tip of the injection cylinder 1 and the tip of the screw 2 in the measuring process. This is the screw retreating force generated by the internal pressure, and this pressure acts directly on the tip of the screw 2 as a reaction force. Also,
The reaction force Fc is a reaction force in the anti-measuring direction that acts on the flight portion of the screw 2 as the resin is conveyed or plasticized in the injection cylinder 1. For example, the tip end of the injection cylinder 1 is caused by the metering rotation of the screw 2. It is generated as a reaction force such as viscosity and transfer resistance of the molten resin fed into, and the size of Fc itself is, for example, the ease of plasticization such as whether the pellet is a virgin pellet or a recycled material, and
It changes variously due to disturbances such as differences in properties such as the size and external shape of pellets. Therefore, like the conventional back pressure control method, Fa = Fb +, which is the overall reaction force acting on the screw 2, that is, the screw back pressure.
Even if the value of Fc is detected by the pressure detector 4 and the thrust of the screw 2 is controlled so as to keep the value of Fa itself constant, the value of Fc can be varied, so that the value of Fb is kept constant. There is no guarantee that it will be.

The control unit 10 of the injection molding machine includes a CNC CPU 25 which is a numerical control microprocessor, a PMC CPU 18 which is a programmable machine controller microprocessor, a servo CPU 20 which is a servo control microprocessor, and CPU 17 for pressure monitoring for performing sampling processing of injection holding pressure and screw back pressure Fa via the A / D converter 16
By selecting mutual input / output via the bus 22, information can be transmitted between the microprocessors.

The PMC CPU 18 is connected to a ROM 13 which stores a sequence program for controlling the sequence operation of the injection molding machine, a program for stabilizing the internal pressure of the reservoir, and a RAM 14 used for temporary storage of calculation data. Further, the CNC CPU 25 is connected to a ROM 27 storing a program for controlling each axis of the injection molding machine and a RAM 28 used for temporary storage of operation data.

Each of the servo CPU 20 and the pressure monitor CPU 17 has a ROM 21 storing a control program dedicated to servo control, a RAM 19 used for temporary storage of data, and a control for sampling processing for obtaining pressure data and the like. R that stores the program
An OM 11 and a RAM 12 used for temporary storage of data are connected. Further, the servo CPU 20 has the CP
Based on a command from U20, a servo amplifier 15 for driving a servo motor of each axis for mold clamping, ejector (not shown), injection, screw rotation, etc. is connected and provided for injection servo motor M1. Each of the outputs from the speed detector P2 provided in the pulse coder P1 and the screw rotation servomotor M2 is fed back to the servo CPU 20, and the current position and movement of the screw 2 calculated by the servo CPU 20 based on the feedback pulse from the pulse coder P1. The speed and the current value of the rotation speed of the screw 2 detected by the speed detector P2 are stored in the current position storage register and the current speed storage register of the memory 19, respectively.

The interface 23 is an input / output interface for receiving signals from limit switches and operation panels provided in various parts of the injection molding machine and transmitting various commands to peripheral equipment of the injection molding machine. A manual data input device 29 with a display is connected to the bus 22 via a CRT display circuit 26 so that a monitor display screen such as injection holding pressure and screw rotation torque, a function menu selection, and various data input operations can be performed. A numeric keypad for inputting numerical data and various function keys are provided.

The non-volatile memory 24 is a memory for storing molding data for storing molding conditions (injection pressure maintaining condition, measuring condition, etc.) and various set values, parameters, macro variables, etc. relating to the injection molding work. The set back pressure Fai and the screw rotation speed value corresponding to the screw position Si are stored as necessary.

With the above configuration, the CNC CPU 25 distributes pulses to the servo motors of the respective axes based on the control program stored in the ROM 27, and the servo CPU 20 distributes the pulses to the respective axes of the movement commands and the pulse coder P.
1. Based on the position feedback signal and the velocity feedback signal detected by a detector such as the velocity detector P2, servo control such as position loop control, velocity loop control and current loop control is performed as in the conventional case, A so-called digital servo processing is executed.

In the weighing process, the servo CPU 20
The current values of the screw position and the screw rotation torque detected via the PMC are measured every predetermined sampling period Δt.
The relationship between the screw position Si and the screw rotation torque Tri is taken in by the CPU for use 18 and the screw rotation torque waveform storage file of the non-volatile memory 24 as shown in FIG. Each molding cycle is updated and stored. Note that the set back pressure Fai is simply described in the file of FIG. 2 for convenience, and may be stored in another file together with other measurement conditions such as the screw rotation speed. The address in the torque waveform storage file substantially corresponds to the number of times of sampling execution after the start of measurement, for example, the screw position Si of the address i is the screw position at the time point i · Δt after the start of measurement, and the screw rotation torque T
ri is the detected value or command value of the drive current of the screw rotation servomotor M2 at the time of i · Δt after the start of measurement, that is, the screw rotation torque Tri. The torque waveform storage file usually holds the relationship between the screw position and the screw rotation torque in the immediately preceding measuring process, but it is possible to keep the relationship between the screw position and the screw rotation torque several times. It is also possible to obtain the average of the screw position and the screw rotation torque at each sampling time in the measurement step of 1. and update and store the average value in the torque waveform storage file every time the measurement step is completed. Further, the data of a desired weighing process, for example, the average value of the data of several weighing processes when a non-defective product is continuously molded is transferred from the torque waveform storage file to the torque waveform saving file in the non-volatile memory 24. It is possible to save it. The contents of the torque waveform storage file are not automatically rewritten for each weighing process, but the file structure itself is exactly the same as the above-mentioned torque waveform storage file.

When stabilizing control of the internal pressure of the reservoir is performed in the measuring step, the waveform of the reference screw rotation torque is stored in advance in the above-mentioned torque waveform storage file in association with the screw position.

FIG. 3 is a conceptual diagram showing an example of a state in which the monitor display screen of the screw rotation torque is displayed on the display of the manual data input device 29. In the monitor display screen of the screw rotation torque, first, the screw position is set to the horizontal axis S and the screw rotation torque is set to the vertical axis Tr, and stored in either the torque waveform storage file or the torque waveform storage file depending on the operator's selection. A diagram TrS showing the relationship between the screw position Si and the screw rotation torque Tri is displayed graphically. When the torque waveform save file is selected and displayed, the display state of the diagram TrS is always fixed, but when the torque waveform storage file is selected and displayed during continuous molding work. In addition, as the display mode of the diagram TrS, automatic rewriting or overwriting each time one weighing process is completed can be selected.

Further, while the data stored in the torque waveform storage file is displayed on the display as shown in FIG. 3, the cursor movement key or the like is operated to perform an appropriate setting work, so that a desired portion can be obtained. It is possible to set the section in which the stabilization control of the internal pressure of the reservoir should be performed.

In this case, when the operator who sets the control section operates the cursor right movement key or the cursor left movement key of the manual data input device 29, the CP for PMC
U18 increments or decrements the value of the address search index i according to the operation of the cursor movement key,
The values of the screw position Si and the screw rotation torque Tri are read from the address i of the torque waveform save file,
A cursor is displayed at the (Si, Tri) spot in (horizontal axis S, vertical axis Tr) on the monitor display screen of the screw rotation torque as shown in FIG. As a result, the cursor moves to the right along the line TrS according to the operation of the cursor right movement key, and moves to the left along the line TrS according to the operation of the cursor left movement key. become.

Therefore, the operator who has decided the section in which the stabilization control of the internal pressure of the reservoir should be carried out first moves the cursor to the starting point P of the screw position section and operates the starting point definition key of the manual data input device 29. The value of the address search index i is stored in the non-volatile memory 24 as the start point address P of the control section, the cursor is moved to the end point Q of the screw position section, and the end point definition key of the manual data input device 29 is operated. The value of the address search index i at that time is stored in the nonvolatile memory 24 as the end point address Q of the control section.

FIG. 4 is a diagram F showing the relationship between the value Fai obtained by multiplying the set back pressure by the screw cross-sectional area and the screw position Si.
aS, screw retraction force Fb generated by reservoir internal pressure
i is a diagram FbS showing the relationship between the screw position Si and the reaction force Fci and the screw position Si, which are variable factors.
According to the diagram FcS showing the relationship with
It is a conceptual diagram which shows an example of the average value of the data of several measurement processes when the back pressure in i is maintained at the setting value Fai / A (A: screw cross-sectional area) and a good product is continuously molded. Among these, the value of the reaction force Fci is a calculated value obtained from the screw rotation torque Tri of the torque waveform storage file of FIG. 2 based on the above-described relational expression of Fci = a · Tri, and
The value of the screw retracting force Fbi generated by the internal pressure of the reservoir is a calculated value obtained by substituting the set value of Fai and the calculated value of Fci into the relational expression of Fai = Fbi + Fci.

If a non-defective product is molded in this state, the value of the screw retreating force Fbi generated by the substantial internal pressure of the reservoir corresponds to the screw position Si in the subsequent metering process, and the diagram of FIG. It is desirable to change along FbS, and it is necessary to reproduce this waveform FbS as much as possible. However, as described above, the value of the reaction force Fci may fluctuate due to various disturbance factors in the subsequent measurement process, so that simply holding the set back pressure Fai / A at a predetermined value causes the internal pressure of the reservoir. The value of the screw retraction force Fbi is shown in FIG. 4 as [Fai-Fc
i] cannot be held.

That is, in the subsequent measuring step, the value of the screw rotation torque becomes Trn at the screw position Si where the screw rotation torque should become Tri, and [Tri-
If a torque deviation of [Trn] occurs, the reaction force Fcn in the counter-measurement direction that occurs at this time is a · Trn, and therefore, [Fn] between the reference reaction force Fci in the counter-measurement direction and F
ci−Fcn] = a · (Tri−Trn) pressure deviation ε
In order to keep the screw retracting force generated by the internal pressure of the reservoir at the reference value Fbi, the screw back pressure value is changed from the reference value Fai [F
ai-ε], that is, [Fai-a · (Tri-Tr
n)] must be corrected. Note that FIG. 4 shows the case of the deviation ε of Fcn <Fci, that is, Trn <Tri, and the value of the back pressure at the screw position Si is reduced from the reference back pressure Fai to [Fai-ε], so that the reservoir internal pressure is changed. This is an example in which the generated screw retracting force is held at the reference value Fbi. Needless to say, if Trn> Tri, ε = [a · (Tri-Tr
n)] is a negative value as a whole, and the screw position S
The value of the back pressure at i is changed from the reference back pressure Fai to [Fai-
By increasing [.epsilon.], the screw retracting force generated by the internal pressure of the reservoir is maintained at the reference value Fbi.

FIG. 6 is a flow chart showing the outline of the reservoir internal pressure stabilizing process adopted in this embodiment to apply the method of the present invention. The control program of the ROM 13 is executed during the measuring process in each molding cycle. Based on
It is repeatedly executed by the PMC CPU 18 at predetermined intervals.

Therefore, the PMC CPU 18 which has started the reservoir internal pressure stabilizing process at every predetermined cycle firstly performs the servo C
The current position S of the screw 2 is read via the PU 20 (step a1), the address P and the address Q of the torque waveform save file in the non-volatile memory 24 are referred to, and the control sections SP to SQ stored in the torque waveform save file are read.
It is determined whether or not there is a screw current position S between (step a2).

The current screw position S is in the control section SP to S
If it is not between Q (the determination result of step a2 is false), P
The MC CPU 18 performs the same measurement control as that of the related art, that is, the reference set back pressure Fai (where i is the value of the address corresponding to the current screw position) set and stored in the non-volatile memory 24 corresponding to the current screw position S. Is output) and the screw rotation speed command is output to the servo CPU 20 based on the screw rotation speed, and the injection servomotor M1
And the screw rotation servomotor M2 is drive-controlled to perform normal metering control (step a9), and the reservoir internal pressure stabilization process of this cycle is completed.

Further, the current screw position S is in the control section S
If it is between P and SQ (the determination result of step a2 is true), the PMC CPU 18 sets the address P corresponding to the start point of the control section in the address search index i (step a3), and from the torque waveform save file. The screw position Si and the screw position Si + 1 are read, and it is determined whether or not the current screw position S is included in this divided section Si to Si + 1 (step a4).

If the current screw position S is not included between the divided sections Si to Si + 1, the PMC
The CPU 18 sequentially increments the value of the address search index i until the divided sections Si to Si + 1 including the current screw position S are detected (step a5), and repeatedly executes the same processing as described above to determine the current screw. The divided sections Si to Si + 1 including the position S are detected (step a
4) Based on the value of the address search index i at that time, the metering control for stabilizing the internal pressure of the reservoir is started.

The PMC CPU 18, which has started the metering control for stabilizing the internal pressure of the reservoir, first sets the servo CPU 20.
The current value Trn of the screw rotation torque is read via and the divided section Si including the current screw position S
The value of the reference value Tri of the screw rotation torque preset for Si + 1 is read from the torque waveform save file based on the value of the address search index i (step a
6), the reference reaction force Fci in the counter-measurement direction and the actual reaction force F according to the above-described calculation formula [a · (Tri-Trn)]
The pressure deviation ε from cn is obtained (step a7). Since the reference reaction force Fci itself is only a theoretical element in the calculation process, all the waveforms shown in FIG. 4 are not stored in this embodiment, and the screw rotation torque Trn and the current screw at the present time are not stored. Based on the reference value Tri of the screw rotation torque stored in the torque waveform storage file corresponding to the position and the constant a obtained by the experiment, the calculation for obtaining ε is performed each time.

PMC CPU 18 for obtaining the pressure deviation ε
Is the divided section Si including the current screw position S.
-Si + 1 is corrected by adding-[epsilon] to a preset back pressure reference set value Fai, and the corrected back pressure [Fai]
The value of the back pressure command of −ε] and the value of the predetermined screw rotation speed command are output to the servo CPU 20 to compensate the fluctuation of the screw retracting force caused by the internal pressure of the reservoir caused by the change of the current value Fcn of the screw reaction force. The injection servomotor M1 is driven to control the back pressure in order to maintain the screw retracting force generated by the reservoir internal pressure at the ideal value Fbi at the time of molding a good product (step a8), and the reservoir internal pressure stabilization process of this cycle is completed.

Thereafter, the PMC CPU 18 determines whether or not the current screw position S is between the control sections SP and SQ at that time until the measurement step is completed, in the same manner as described above, until the measurement step is completed. Alternatively, the metering control for stabilizing the internal pressure of the reservoir is repeatedly executed.

As described above, the value of the back pressure command increases as the current value Fcn of the screw reaction force increases, and
As a result of the back pressure command value decreasing in accordance with the decrease in the current value Fcn of the screw reaction force, the screw reaction force Fcn due to disturbance is generated.
Is absorbed, and the screw retracting force generated by the internal pressure of the reservoir is held at an ideal value Fbi corresponding to the screw position Si.

As described above, as one embodiment, the reference back pressure is set based on the pressure deviation ε between the actual reaction force Fcn in the counter-measurement direction and the reference reaction force Fci in the counter-measurement direction. Although the case where the correction is applied to Fai has been described, the screw retracting force Fbn generated by the actual reservoir internal pressure and the screw retracting force F generated by the reference reservoir internal pressure are described.
Even if the calculation is performed based on the pressure deviation α with respect to bi, the final calculation result is exactly the same as the above.

That is, α = Fbi-Fbn = Fbi- (Fai-Fcn) = Fbi- (Fai-a.Trn) = (Fai-a.Tri)-(Fai-a.Trn) =-a. (Tri -Trn) =-[epsilon], and the sign is inverted here, the reaction force F in the counter-measurement direction based on the reaction force Fcn in the counter-measurement direction.
When it increases with ci as a reference, the screw retraction force Fbn generated by the actual internal pressure of the reservoir decreases, so the value of the back pressure command is increased (Fcn> Fci is corrected to increase the back pressure), but it becomes the reference. When the screw retreating force Fbn generated by the reservoir internal pressure increases with respect to the screw retreating force Fbi generated by the reservoir internal pressure, the value of the back pressure command is reduced (corrected in the direction of reducing the back pressure when Fbn> Fbi). It's just saying.

Instead of setting the reference value Fai of the back pressure, the target value of the screw retreating force Fbi generated by the internal pressure of the reservoir is stored in the non-volatile memory 24 as it is, as shown in FIG. It is set, and F is set according to the screw position in the process of step a6.
Bi and Trn are read, and [a.Tr
n], that is, the value of Fcn, and the value of [Fbi + a · Trn] is output as the back pressure command in the process of step a8, the same result is obtained.

[0045]

According to the reservoir internal pressure adjusting method of the present invention, the deviation of the screw rotation torque is detected to detect the change of the disturbance acting in the anti-metering direction on the screw. It is possible to detect fluctuations in the internal pressure of the reservoir indirectly and accurately without installing a pressure detector in the cylinder. Furthermore, by changing the screw back pressure according to the deviation of the screw rotation torque, the influence of disturbance can be reduced. Since it is possible to pressurize the resin in the reservoir with the removed thrust, the internal pressure of the reservoir can be appropriately maintained regardless of the fluctuation of the disturbance. As a result, the properties of the molten resin measured in the reservoir are stable, and it is possible to perform injection molding work with few molding defects.

[Brief description of drawings]

FIG. 1 is a block diagram showing a main part of an injection molding machine of an embodiment to which a method for adjusting a reservoir internal pressure according to the present invention is applied.

FIG. 2 is a conceptual diagram showing the configurations of a screw rotation torque waveform storage file and a torque waveform storage file used in the reservoir internal pressure stabilization process of the same embodiment.

FIG. 3 is a schematic diagram showing a display example of a monitor display screen displaying a screw rotation torque waveform.

FIG. 4 is a value Fa obtained by multiplying a set screw back pressure by a screw cross-sectional area, and a screw retracting force F generated by a reservoir internal pressure.
FIG. 3B is a conceptual diagram showing an example of the relationship between b and the screw reaction force Fc with the screw position as a reference.

FIG. 5 is a diagram schematically showing another file used for stabilizing the internal pressure of the reservoir.

FIG. 6 is a flowchart showing an example of reservoir internal pressure stabilization processing.

[Explanation of symbols]

 1 Injection Cylinder 2 Screw 4 Pressure Detector 10 Control Device 18 PMC CPU 24 Nonvolatile Memory 29 Manual Data Input Device (Graphic Display)

Claims (3)

[Claims] 1. In an injection molding machine in which a screw is driven at a back pressure and a screw rotation speed set corresponding to a screw position to perform a measuring process, a screw rotation torque in a measuring process during molding of a good product is measured by a screw. Corresponding to the position, it is preset and stored in the controller of the injection molding machine, the current value of the screw rotation torque is sequentially detected in the weighing process, and preset and stored in the controller of the injection molding machine corresponding to the current screw position. An injection molding machine characterized by stabilizing a reservoir internal pressure of an injection cylinder by obtaining a deviation between the generated screw rotation torque and a current value of the screw rotation torque, and changing the set back pressure based on the torque deviation. Method for adjusting internal pressure of reservoir. 2. In an injection molding machine in which a screw is driven at a screw rotation speed set corresponding to a screw position to perform a measuring step, the relationship between the screw reaction force generated by the screw rotation torque and the screw rotation torque. , And the relationship between the reservoir internal pressure and the screw position is preset and stored in the control device of the injection molding machine, the current value of the screw rotation torque is sequentially detected in the measuring process, and the current screw is based on the function. The reaction force is calculated, and the sum of the screw reaction force and the screw retraction force calculated from the reservoir internal pressure that is preset and stored in the controller of the injection molding machine corresponding to the current screw position is output as the screw retraction force during measurement. The internal pressure of the reservoir of the injection molding machine is characterized by stabilizing the internal pressure of the reservoir of the injection cylinder. Pressure adjustment method. 3. A reservoir for an injection molding machine according to claim 2, wherein a function indicating a relationship between a screw reaction force generated by the screw rotation torque and the screw rotation torque is set and stored as a proportional expression in a controller of the injection molding machine. Internal pressure adjustment method.